There is considerable clinical evidence to suggest that morphological changes occur in the cornea as a result of hard contact lens wear. These are manifested by abnormal changes in a patient's refraction, keratometry and visual acuity. It has been claimed that hydrogel and other flexible contact lenses produce fewer corneal changes in flexible contact lens patients. Measurements by photokeratoscopy and corneal thickness measurements by pachometry will be used to differentiate between corneal edema or other sources of irritation caused by contact lenses. In addition I will study the oxygen transmission through a contact lens in order to determine the effects of the lens on normal corneal physiology.